1. Field of the Invention
This invention relates to a drying device for drying recording paper printed by an ink jet head.
2. Description of the Prior Art
In the ink jet printer, characters or images are formed on recording paper by discharged ink. Recently, slow dry black ink has been used to obtain high character image quality, and on the other hand, the print speed has been more and more accelerated. Therefore, incomplete dryness of ink is liable to occur, so it is necessary to quickly dry ink by a drying device.
As shown in FIG. 13, in a drying device 100 disclosed in Japanese Published Unexamined Patent Application No. Hei 8-224871, the upper surface of a single infrared heater 102 is covered with a dome-like hood 104, and a reflector 106 is disposed between the infrared heater 102 and the hood 104.
The drying device 100 is provided with an exhaust fan 108, and the interior pressure of the hood 104 is negative. An inlet port 104A is formed in the hood 104, and the outside air sucked through the inlet port 104A is guided toward recording paper P to dry the recording paper P by radiation heat by the infrared heater 102 and warmed outside air.
The outside air sucked through the inlet port 104A falls straight down toward the recording paper P, and then branches off to the upstream side and the downstream side in the transport direction of the recording paper P to be passed through a gap between the recording paper P and the lower end face 112A of the inner wall 12 of a housing 110 and be guided to the exhaust fan 108 by a blowing space formed between the inner wall 112 and the outer wall 114.
However, since only the single infrared heater 102 is used, the distribution of heat energy received by the recording paper P surface is not uniform, and the interior of the housing 110 of the drying device 100 has a complicated form, so that when the outside air is guided from the lower end face 112A of the inner wall 112 onto the surface of the recording paper P, the ventilating area of the blowing space changes considerably to generate a turbulent flow, resulting in variation in distribution of wind velocity on the recording paper P surface.
Therefore, even if the heat energy amount received by the moving recording paper P surface is set uniform at each point, that is, the distribution of heat radiation energy on the recording paper P surface is set uniform, the temperature (distribution of energy received by the recording paper P) of the recording paper P varies, so that an incompletely dried portion is caused. Accordingly, to evenly drying the recording paper P, it is necessary to increase the radiation heat amount (heat radiation energy) of the infrared heater 102.
Further, it is apprehended that if the recording paper P is exposed to a large amount of radiation heat for a long time due to the occurrence of a jam of the recording paper P in the drying device, scorching or fuming is caused.
The present invention has been made in view of the above circumstances and provides a drying device capable of evenly drying recording paper by keeping the temperature of the moving recording paper substantially constant without any increase in the heat radiation amount (heat radiation energy).
According to an aspect of the present invention, the drying device has a heating element for drying recording paper printed by an ink jet head. Below the heating element, a platen to which the recording paper is transported is disposed, and the radiation heat of the heating element is reflected toward the platen by a reflector.
Further, a space is formed between the heating element and the platen surface, and an airflow is generated in the space by an airflow generating unit. On the other hand, an energy adjusting unit is provided to keep the temperature of recording paper moved in the space substantially constant.
By this arrangement, in the case where the wind velocity of the airflow is constant in the space, for example, comparing between the upstream and the downstream in the drying region (space), the surface temperature of the recording paper is also lower and also the temperature of the outside air blown into the drying region is lower on the upstream, so that the radiation heat amount is made larger on the upstream than on the downstream. Thus, the radiation heat amount is adjusted so that the temperature of moving recording paper is substantially constant both on the upstream and on the downstream in the drying region.
In the case where the velocity of the airflow is different in the drying region, the radiation heat amount in the higher velocity region is made larger than that in the lower velocity region. Thus, the radiation heat amount is varied according to the velocity of the airflow or the like so that the recording paper is evenly dried and when a recording paper jam occurs in the drying device, there is no possibility of scorching, fuming or the like.
According to another aspect, the drying device has plural heating elements disposed along the transport direction of recording paper, and the output of the individual heating element is varied to adjust the radiation heat amount.
Thus, the plural heating elements are disposed in the transport direction of recording paper, whereby as compared with the case of drying recording paper with a single recording element, near infrared rays and radiation heat are not concentrated so that the recording paper is evenly dried. Further, the output of an individual heating element is made differ so that the temperature of the recording paper moved in the drying region is substantially constant.
According to another aspect of the invention, the drying device has plural heating elements disposed along the transport direction of recording paper and respectively varied in the clearance from a platen so that the temperature of recording paper moved in the drying region is substantially constant.
According to another aspect of the invention, the drying device has plural heating elements disposed along the transport direction of the recording paper, and the space between the heating elements is varied so that the temperature of recording paper moved in the drying region is substantially constant.
According to another aspect of the invention, the distance of a reflector from the platen is varied so that the temperature of recording paper moved in the drying region is substantially constant.
According to another aspect of the invention, the drying device has plural heating elements disposed along the transport direction of the recording paper. The heating elements are divided into each heating element by partition plates, and the respective heating elements are demarcated. Therefore, even with the heating elements having the same output, the demarcating size is varied to adjust the amount of radiation heat applied to moving recording paper.
According to another aspect of the invention, the drying device has a heating element disposed in a housing demarcating the drying region for drying recording paper printed by an ink jet head. Below the heating element, a platen to which the recording paper is transported is disposed, and the radiation heat of the heating element is reflected toward the platen by a reflector.
Further, a space is formed between the heating element and the platen, and an airflow is generated in the space by an airflow generating unit.
On the other hand, an airflow rectification unit is provided opposite to the platen in the space, and an airflow is rectified by the airflow rectification unit. Therefore, the wind velocity in the drying region becomes constant so that the recording paper is evenly dried.
As an airflow generating unit, an intake fan, for example, is provided and the taken outside air is abutted to the housing, and the outside air is flowed into the space formed by the housing and the reflector to prevent overheat of the heating element and restrain a temperature rise in the drying region. Further, an exhaust fan is provided to quickly discharge moist air touching the print surface of the recording paper, so that dew condensation in the housing can be prevented.
According to another aspect of the invention, the velocity of the airflow rectified by the airflow rectification unit is set 1 m/sec or faster. Thus, the airflow is passed on the surface of recording paper at a rate of 1 m/sec, whereby even in the case where a jam of recording paper occurs in the drying device and the recording paper is exposed to radiation heat for a long time, the recording paper is kept from overheating so that scorching, fuming or the like can be prevented.
According to another aspect of the invention, the ventilation area on the downstream side of the blowing space formed between the airflow rectification unit and the platen is made smaller than that on the upstream side.
Thus, even if the loss of fluid energy is caused as it goes downstream in the drying region by a resistive material such as a star wheel or the like disposed in the drying region, lowering of velocity of the airflow can be prevented by reducing the ventilation area on the downstream.
According to another aspect of the invention, the airflow rectification unit is a plate having an infrared ray transmittance of 90% or more. Therefore, the loss of heat radiation energy on recording paper surface can be restrained so that the heat radiation energy required for drying can be used efficiently.
According to another aspect of the invention, the plate is heat resisting glass. Since the heat resisting glass has a high thermal deformation temperature, problems such as cracks or deformation are not caused even in the drying region.
According to another aspect of the invention, the drying device includes heating elements provided in a housing demarcating the drying region for drying recording paper printed by an ink jet head, a platen disposed below the heating elements, to which the recording paper is transported, and a reflector for reflecting the radiation heat of the heating elements toward the platen, and the drying device further includes an airflow generating unit that generates an airflow in a space formed between the heating elements and a surface of the platen, an airflow rectification unit provided opposite to the platen in the space that rectifies the airflow, and an energy adjusting unit that keeps substantially constant the temperature of the recording paper moved in the space. Accordingly, the effects of the invention can be obtained, and as the drying device of the invention has the airflow rectification unit that rectifies an airflow, the energy adjusting unit is capable of stably adjusting the heat radiation energy much more easily and quickly than the drying device without the airflow rectification unit, so that the temperature of recording paper moved in the space can be substantially constant.